This invention is related to sample injection systems for gas chromatographs and other similar analyzer devices, and more specifically to a sample injection system using a source of vacuum to obtain the sample.
There are several desirable requirements which should be met for a sample injection system. To achieve reliable, reproducible results, the sampling system should be able to inject a reproducible molecular quantity of sample each time. The injection system should also be designed to permit impurities to be washed out of the system before a sample is injected, so that the possibility of contamination of the sample from a previous sample is minimized. Preferably, the sampling system should be versatile enough so that it can receive samples contained at less than atmospheric pressure, as well as above. Another requirement for a sampling system is that it should be designed for efficient use of the sample by minimizing the amount of sample wasted and the amount of sample required for washing out the sampling system. In some instances, it is desirable that the sample injection system be designed so that it can be automated, so that continuous testing can be conducted as well as for obtaining better reproducability of results.
One of the problems today is that many of the sample injection systems available in the prior art fail to achieve all of the above noted requirements. One system in the prior art is a gas sampling valve in which the volume is trapped in a passage in the valve and quickly introduced into the carrier gas flow. In this system, temperature and volume can be accurately determined, but since the pressure is related to the flow rate, it often cannot be determined as accurately as is required. This system also fails to meet the requirements of sampling efficiency and the problems of being able to work with samples at less than atmospheric pressure.
Another method of obtaining a sample volume and injecting it in an anaylzer is to use the gas type syringe. This sampling system has problems meeting the requirements for reproductability of the sample size, because of the small volumes needed for analyzers, as well as the desirability that the system be easily adaptable to sample automation.